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Components of a typical, four stroke cycle, DOHC piston engine. (E) Exhaust camshaft, (I) Intake camshaft, (S) Spark plug, (V) Valves, (P) Piston, (R) Connecting rod, (C) Crankshaft, (W) Water jacket for coolant flow.

A piston is a component of reciprocating engines, pumps and gas compressors. It is located in a cylinder and is made gas-tight by piston rings. In an engine, its purpose is to transfer force from expanding gas in the cylinder to the crankshaft via a piston rod and/or connecting rod. In a pump, the function is reversed and force is transferred from the crankshaft to the piston for the purpose of compressing or ejecting the fluid in the cylinder. In some engines, the piston also acts as a valve by covering and uncovering ports in the cylinder wall.

Piston engines

Main article: Reciprocating engine

Internal combustion engines

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There are two ways that an internal combustion piston engine can transform combustion into motive power. These are the two-stroke cycle and the four-stroke cycle. A single cylinder two-stroke engine produces power every crankshaft revolution, while a single cylinder four-stroke engine produces power once every two revolutions. Older designs of small two-stroke engines produced more pollution than four stroke engines. However, modern two-stroke designs, like the Vespa ET2 Injection utilise fuel-injection and are as clean as four-strokes. Large diesel two-stroke engines, as used in ships and locomotives, have always used fuel injection and produce low emissions. One of the biggest internal combustion engines in the world, the Wärtsilä-Sulzer RTA96-C is a two-stroke; it is bigger than most two-story houses, has pistons nearly 1 metre in diameter and is one of the most efficient mobile engines in existence. In theory, a four-stroke engine has to be larger than a two-stroke engine to produce an equivalent amount of power. Two-stroke engines are becoming less common in developed countries these days, mainly due to manufacturer reluctance to invest in reducing two-stroke emissions. Traditionally, two-stroke engines were reputed to need more maintenance (despite exceptions like the Ricardo Dolphin engine, and the Twingle engines of the Trojan car and the Puch 250 motorcycle). Even though the simplest two-stroke engines have fewer moving parts, they could wear out faster than four-stroke engines. However fuel-injected two-strokes achieve better engine lubrication, and cooling and reliability should improve considerably.

Gallery

A piston and its connecting rod.

CAD drawing of crankshaft and pistons.

Large pistons (over 0.5 m incl. connecting rod).

Simplified piston animation.

Steam engines

Steam engines are usually double-acting (i.e. steam pressure acts alternately on each side of the piston) and the admission and release of steam is controlled by slide valves, piston valves or poppet valves.

Air cannons

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There are two special type of pistons used in air cannons: close tolerance piston and double piston. While in close tolerance piston, O-rings are used as valve but in double piston, O-rings are not used.

There are some features of close tolerance piston mentioned below:

1. Piston can swell and stick.
2. Fits tightly in the cylinder.
3. Tight Tolerance fit.
4. Properties alter due to atmospheric change.
5. Backlash may such,some of the bin material into the valve which also can cause the piston to stick.

Common features of double piston:

1. Cannot swell and stick.
2. Fits loosely in the cylinder.
3. No tight tolerance fit.
4. Properties are not altered due to atmospheric change.
5. Even if foreign material enters the valve,the double piston does not stick.

Drawbacks

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Since it’s a main reciprocating part of engine and hence it create the problems of unbalancing due to its inertia. Due to friction between wall of the cylinder and piston rings its life becomes short and it generates the unpleasant sound due reciprocating mechanism. To transmit the energy of reciprocating piston, it is connected to a connecting rod and crank mechanism and due to these part there occurs mechanical loss. The motion of the crank shaft is not smooth, since energy supplied by the piston is not continuous and it is impulsive in nature. To supply the fuel into the cylinder there is need of the valves and valve mechanism and during opening and closing & the valve mechanical noise occurs also mechanical vibration.

See also

Look up Piston in
Wiktionary, the free dictionary.

• Piston ring
• Air gun
• IRIS engine
• Flamethrower
• Fruit press
• Hydraulic cylinder
• Knurling
• Slide whistle
• Wankel engine (an internal combustion engine with a rotary 'piston')
• Steam locomotive components
• Rocket engine nozzle effectively forms the piston for rockets

References

External links

Wikimedia Commons has media related to:

Piston

• Piston highlight: Hypervideo of construction and operation of four cylinder internal combustion engine courtesy of Ford Motor Company

Wikipedia content modification information:

• This page was last modified on 10 November 2008, at 21:20.

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